Various patents of prior art teach methods and devices for the detection of electrically conductive particles suspended in a moving, electrically nonconductive liquid. Especially important is the detection of particles in lubrication systems resulting from the wear and tear of mating mechanical moving parts, such as in internal combustion engines, turbines and comparable ground support and airborne power plants and accessories.
Because particles of the described nature may, firstly, be of either ferrous or nonferrous substances, different methods must be employed to capture all those particles; secondly, considering the possible presence of physically large particles of either composition, a separate and additional detection element appears to be required.
These teachings, which do not cover the entire domain of the particle detection practice, include, but may not be limited to, the following examples and references, presenting at least one typical antecedent for each individual function of possible relevance:
______________________________________ Bowser 1,176,732 March 28, 1916 (none) Matheson 2,010,435 Aug. 6, 1935 (210-43) Lincoln 2,016,642 Oct. 8, 1935 (183-2.7) Schrader 2,349,992 May 30, 1944 (175-183) Scott 2,375,826 May 15, 1945 (92-28) Bourne, Jr. 2,429,920 Oct. 28, 1947 (177-311) Bourne, Jr. 2,450,630 Oct. 5, 1948 (200-52) Vokes 2,544,244 March 6, 1951 (210-166) Botstiber 2,704,156 March 15, 1955 (210-1.5) Botstiber 2,936,890 May 17, 1960 (183-86) Winslow 2,952,330 Sept. 13, 1960 (183-2.5) Botstiber 2,983,385 May 9, 1961 (210-222) Hurby 3,067,876 Dec. 11, 1962 (210-65) Winslow 3,127,255 Mar. 31, 1964 (55-178) Botstiber 3,317,042 May 2, 1967 (210-86) Botstiber 3,432,750 Mar. 11, 1969 (324-41) Kudlaty 3,628,662 Dec, 21, 1971 (210/136) Miller 3,686,926 Aug. 29, 1972 (73/61R) Miller 3,878,103 Apr. 15, 1975 (210/243) Tauber 4,199,443 Apr. 22, 1980 (210/85) Tauber 4,282,016 Aug. 4, 1981 (55/204) ______________________________________
The foregoing enumeration of prior art indicates that, while specific significant features are present in various teachings, the operationally required wide performance characteristics of the subject invention can not be observed in that prior art.
Reviewing the prior art more selectively, in U.S. Pat. No. 3,317,042 both a method and a device are described for the detection of electrically conductive particles in a moving liquid. In that invention, a screen, or filter is used to guide the particles towards electrical contacts which, when bridged by one or more conductive particles, will close an electric circuit. Other patents, such as U.S. Pat. Nos. 3,686,926 and 3,878,103 use a screen in which the fibers are of conductive materials, alternatingly connected to electrical lines of different polarities and separated from each other by insulating members. All these devices have the deficiency of insufficient contact pressure of the particles on the electrically conductive members of the detecting device; the particles are small and light in weight; buoyancy in the liquid acts to aggravate this condition and as a result, the contact pressure is too low to produce a reliable electric circuit. For ferrous, i.e., magnetizable particles, this deficiency can be alleviated by combining the detector contacts with a magnet, as in U.S. Pat. Nos. 2,936,890 and 3,432,750. Of these, the former applies to ferrous particles only, the latter uses the magnetic effect to attract ferrous particles, while nonferrous particles are still subject to the above-mentioned deficiency in detection. The devices based on alternatingly connected screens do not offer the contact pressure increasing effect of magnetism; they detect ferrous as well as nonferrous particles indiscriminately, with the above-mentioned shortcoming in contact conductive effect. Also, they have the disadvantage of requiring large areas of such alternatingly connected, separately insulated grids or weaves, with the resulting high manufacturing cost, unstable construction and difficulty in identifying and removing particles that have become lodged in the grid, or weave.
Most applications for this type of device relate to fluid systems, such as the lubrication oil circuits of engines and mechanical power transmissions, or the liquid systems of hydraulic power and control units. In these, it is desirable to ignore the very small particles produced by normal wear of moving parts, while capturing and indicating the presence of larger particles which are either of alien nature to the system, or are indicative of incipient gradual deterioration and eventual failure of such moving parts. The screens used in the above-mentioned patents may be selected to pass fine and harmless wear particles, while retaining for indication the larger particles. These, however, will then be subject to the above-mentioned problem of insufficient electrical contact pressure and conductivity.
In U.S. Pat. No. 4,282,016 a device is described, which separates particles and air from a flowing liquid by subjecting both substances to a centrifugal force of rotation of the liquid. In this system, the separating effect for small, normal wear particles is absent. A particle sensor introduced into a device according to that patent will not indicate nonferrous particles, but will have to rely on the magnetic effect for ferrous particles only, such as in U.S. Pat. No. 2,936,890. It would be possible to equip such devices with self-closing particle sensors, such as described in U.S. Pat. Nos. 2,704,156 and 2,983,385. The above-mentioned particle detectors of the screen type, namely, U.S. Pat. Nos. 3,686,926 and 3,878,103, do not offer the advantageous use of such self-closing sensor arrangements, which make them impractical for removal and inspection of captured particles, a feature which is of utmost importance in all systems which do not permit shut-down and drainage of the fluid system during operation.